Baidya Tinku, Gayen Arup, Hegde M S, Ravishankar N, Dupont Loic
Solid State and Structural Chemistry Unit and Material Research Centre, Indian Institute of Science, Bangalore, India.
J Phys Chem B. 2006 Mar 23;110(11):5262-72. doi: 10.1021/jp0565103.
Nanocrystalline Ce(1)(-)(x)Ti(x)O(2) (0 < or = x < or = 0.4) and Ce(1-)(x)(-)(y)Ti(x)Pt(y)O(2)(-)(delta) (x = 0.15, y = 0.01, 0.02) solid solutions crystallizing in fluorite structure have been prepared by a single step solution combustion method. Temperature programmed reduction and XPS study of Ce(1)(-)(x)Ti(x)O(2) (x = 0.0-04) show complete reduction of Ti(4+) to Ti(3+) and reduction of approximately 20% Ce(4+) to Ce(3+) state compared to 8% Ce(4+) to Ce(3+) in the case of pure CeO(2) below 675 degrees C. The substitution of Ti ions in CeO(2) enhances the reducibility of CeO(2). Ce(0.84)Ti(0.15)Pt(0.01)O(2)(-)(delta) crystallizes in fluorite structure and Pt is ionically substituted with 2+ and 4+ oxidation states. The H/Pt atomic ratio at 30 degrees C over Ce(0.84)Ti(0.15)Pt(0.01)O(2)(-)(delta) is 5 and that over Ce(0.99)Pt(0.01)O(2)(-)(delta) is 4 against just 0.078 for 8 nm Pt metal particles. Carbon monoxide and hydrocarbon oxidation activity are much higher over Ce(1-)(x)(-)(y)Ti(x)Pt(y)O(2) (x = 0.15, y = 0.01, 0.02) compared to Ce(1)(-)(x)Pt(x)O(2) (x = 0.01, 0.02). Synergistic involvement of Pt(2+)/Pt degrees and Ti(4+)/Ti(3+) redox couples in addition to Ce(4+)/Ce(3+) due to the overlap of Pt(5d), Ti(3d), and Ce(4f) bands near E(F) is shown to be responsible for improved redox property and higher catalytic activity.
采用一步溶液燃烧法制备了在萤石结构中结晶的纳米晶Ce(1)(-)(x)Ti(x)O(2)（0≤x≤0.4）和Ce(1-)(x)(-)(y)Ti(x)Pt(y)O(2)(-)(δ)（x = 0.15，y = 0.01，0.02）固溶体。对Ce(1)(-)(x)Ti(x)O(2)（x = 0.0 - 04）进行的程序升温还原和XPS研究表明，与纯CeO(2)在675℃以下约8%的Ce(4+)还原为Ce(3+)相比，Ti(4+)完全还原为Ti(3+)，约20%的Ce(4+)还原为Ce(3+)。CeO(2)中Ti离子的取代增强了CeO(2)的还原性。Ce(0.84)Ti(0.15)Pt(0.01)O(2)(-)(δ)在萤石结构中结晶，Pt以2+和4+氧化态进行离子取代。在30℃时，Ce(0.84)Ti(0.15)Pt(0.01)O(2)(-)(δ)上的H/Pt原子比为5，Ce(0.99)Pt(0.01)O(2)(-)(δ)上的H/Pt原子比为4，而8nm Pt金属颗粒的H/Pt原子比仅为0.078。与Ce(1)(-)(x)Pt(x)O(2)（x = 0.01，0.02）相比，Ce(1-)(x)(-)(y)Ti(x)Pt(y)O(2)（x = 0.15，y = 0.01，0.02）上的一氧化碳和烃类氧化活性要高得多。由于E(F)附近Pt(5d)、Ti(3d)和Ce(4f)能带的重叠，除了Ce(4+)/Ce(3+)之外，Pt(2+)/Pt°和Ti(4+)/Ti(3+)氧化还原对的协同作用被证明是氧化还原性能改善和催化活性提高的原因。
